The number of reservoirs in Ethiopia is increasing, primarily for hydroelectric power generation, irrigation, and drinking water supply. However, studies focusing on the aquatic life within the reservoirs are scarce and significantly lagging behind the increasing development of these freshwater ecosystems. The community structure, species composition and abundance of zooplankton in relation to physico-chemical changes were investigated in the Omo Gibe III reservoir in 2024. Zooplankton samples were collected using plankton nets and preserved in a solution containing 5% formalin and Lugol’s iodine. Measured physicochemical parameters included a temperature range of 24.30 °C to 31.90 °C, as well as a dissolved oxygen range of 5.4 mg/L to 5.8 mg/L, both of which fall within the optimal range for most zooplankton species. A total of 20 zooplankton species were identified and categorized Rotifera (11 species), Copepoda (5 species), and Cladocera (4 species). The community structure was predominantly represented by Rotifera which accounted for 46.2%, Copepoda for 29.3%, and Cladocera for 24.5%. This study provided valuable insights into the zooplankton community structure of the Omo Gibe III Reservoir, demonstrating how alterations in physicochemical variables can impact species diversity and abundance.

Fishery resources in Nigeria are experiencing a rapid decline, underscoring the urgent need for effective biodiversity surveys and comprehensive species documentation to guide conservation and management efforts. However, traditional methods for fish surveys, such as gillnets and trawl surveys, are intrusive, time-intensive, and costly. Environmental DNA (eDNA) metabarcoding has emerged as a non-invasive method for surveying fish diversity, yet its application in Nigerian aquatic ecosystems remains limited. This study evaluated the potential and limitations of 12S rRNA-based eDNA metabarcoding to survey fish communities across three water bodies (Jebba Hydroelectric Power Dam, Asa River, and Lagos lagoon). We also compared fish community composition obtained from our eDNA samples with previously published inventories based on traditional sampling techniques. Our study revealed several advantages of using eDNA metabarcoding for fish biodiversity surveys in Nigeria, including the rapid and non-invasive identification of fish taxa, the detection of differences in community composition and biodiversity metrics, the identification of species overlooked by traditional methods, and the ability to detect both threatened and invasive species. However, we identified three major constraints that must be addressed for the successful integration of eDNA sampling techniques in Nigeria. First are the logistical challenges, including determining the optimal number of replicates, selecting the appropriate water volume per site, determining the required number of sampling sites per study area, and identifying the most suitable time within the season for sampling. Second is the lack of a comprehensive DNA reference database for accurate species identification. Third are the issues with primer and marker specificity. Until a comprehensive regional DNA reference library is developed, suitable molecular markers are optimized, and standardized field protocols for eDNA sampling are established, we recommend using eDNA metabarcoding as a complementary survey tool rather than a replacement for conventional fish survey methods in Nigeria.

Rivers are vital ecosystems that support biodiversity and provide essential ecosystem services to both man and the environment. A wide range of communities in developing countries, such as Kenya rely on river water for irrigation, domestic use, animal watering, and industrial use leading to contamination and altered ecosystem quality. The study aimed to assess human activities influence on distribution of Ephemeroptera, Plecoptera, and Trichoptera along River Kiminini in Trans-Nzoia County, Kenya. It was conducted in 2023 from July to September covering the wet season. Physical-chemical parameters in water and EPT richness were determined from 10 sampling stations along the river. Macroinvertebrates were collected for taxonomic identification and richness counts. The concentrations of phosphates in all stations were higher than the World Health Organization’s recommended limit of 0.1 mg/l. Stations S1 (12.09 mg/l), S2 (11.77 mg/l), S3 (14.40 mg/l), S7 (10.85 mg/l), and S9 (12.54 mg/l) had nitrate levels above the WHO-recommended threshold of 10 mg/l. The macroinvertebrates analysis revealed 42 macroinvertebrates genera, with EPT dominating the upstream stations and decreasing downstream with increasing levels of physical-chemical parameters influenced by human activities. In view of the downstream reduction in EPT richness with increase in physical-chemical parameters levels, the study highlights the significance of riparian land use control and continuous EPT species monitoring as a crucial measure to reduce water quality deterioration and enhance habitat conditions in general.

Walleye Sander vitreus are economically and ecologically vital to Lake Erie and have multiple spawning stocks that contribute to the lakewide population. These unique Walleye stocks typically spawn in discrete spawning aggregations in riverine and shallow, open-lake reef habitats during springtime in the western, eastern, and central basins. Yet, most spawning research has been conducted in the western and eastern basins. Therefore, the goal of our study was to document evidence of Walleye utilizing a central basin nearshore reef for reproduction. We used gill nets from 20 March to 15 May 2012, on Hardy Point Reef (HPR; near Fairport Harbor, Ohio) to collect spawning Walleye. Larval light traps and egg mats were deployed to capture fertilized eggs and newly hatched larvae. We captured 281 actively spawning Walleye using overnight-set gill nets from HPR. Five fertilized Walleye eggs and two larval Walleye were captured from HPR. Our study provided evidence that successful Walleye spawning occurred at HPR in the central basin of Lake Erie. Further research should identify potential additional Walleye spawning locations in the central basin and quantify these contributions to the Lake Erie population to help facilitate lake wide management and preservation of spawning stocks.

The invasive signal crayfish (Pacifastacus leniusculus), a species of high concern in European freshwaters, represents a substantial threat to native crayfish species and freshwater ecosystems. Its widest distribution in Croatia is observed in the lowland Drava River and the karstic Korana River, where signal crayfish populations have occurred for over a decade. Populations of native noble crayfish and narrow-clawed crayfish have been completely displaced in the long-term invaded sites at both rivers, while drastic reduction of native crayfish has been observed at the active invasion fronts of the Korana River. As the signal crayfish continues to invade new freshwater sections, we aimed to evaluate its diet and trophic niche to assess its trophic dynamics across various invasion stages. We sampled signal crayfish and its major potential food sources at invasion core sites at Drava and Korana Rivers, as well as the active invasion front of the Korana River. Samples were analysed on their stable carbon (δ13C) and nitrogen (δ15N) isotopes to evaluate the signal crayfish food source preferences and trophic niche widths. Our results indicate that its diet preferences and trophic niche are highly dynamic and vary with invasion stage and local environmental conditions. In the Drava River, signal crayfish showed a strong preference for animal-based food sources, coupled with a wide trophic niche width and low intraspecific competition. At Korana River invasion core, high crayfish densities were associated with a contracted trophic niche, and a predominant reliance on periphyton. In contrast a broader trophic niche at the invasion front was observed, showing a more generalist feeding strategy. Additionally, potential predation on the native narrow-clawed crayfish was observed. Our findings highlight the trophic plasticity and adaptability of the signal crayfish, explaining its invasive success, and provide a broader understanding of invasive species dynamics in European freshwaters.

Despite the ecological importance of Sphaeriidae, habitat preferences of Pisidium coreanum and Musculium lacustre in the Republic of Korea remain poorly understood. This study evaluated habitat suitability of both species using two distinct datasets: a targeted fingernail clams survey (58 samples, 2023) and a national biological monitoring program (20,580 samples, 2012–2021). Using twelve probability distribution models (PDMs), including reversed log-normal and Weibull distributions, we derived habitat suitability indices (HSIs) four environmental variables—altitude, water depth, velocity, and mean substrate particle size. Optimal habitat ranges varied notably between surveys: P. coreanum showed thermophobic, rheophobic, and lithophobic traits in the fingernail clams survey but thermophilic, rheophilic, and lithophilic characteristics in the biomonitoring data. Similarly, M. lacustre also displayed variation in habitat traits across datasets. These contrasting ecological profiles reflect methodological differences between surveys: targeted multi-habitat sampling in the fingernail clams survey versus riffle-focused sampling in the biomonitoring program. Our results demonstrate that habitat suitability assessments are sensitive to survey design, potentially leading to conflicting interpretations of species’ ecological niches. Furthermore, combining closely related species (e.g. at the family level) without considering such variation may obscure species-specific habitat signals, especially for small, passively dispersed bivalves like Sphaeriidae. This study provides a framework for applying PDMs in habitat modeling and highlights the importance of aligning data sources with ecological research or conservation goals. Method-aware habitat characterization is essential for improving indicator development, refining conservation strategies, and enhancing interpretation of benthic macroinvertebrate monitoring data.

Gizzard Shad Dorosoma cepedianum are important for nutrient cycling and can affect water clarity, plankton densities, and fish production levels. Gizzard Shad can also be crucial prey fish for recreationally important species such as Walleye Sander vitreus and Smallmouth Bass Micropterus dolomieu. Lake Sharpe, a mainstem Missouri River reservoir located in central South Dakota, supports a recreationally important Walleye and Smallmouth Bass fishery with Gizzard Shad being the primary prey fish. Previous work suggested Hipple Lake, a backwater embayment of Lake Sharpe, may be an important overwinter location for Gizzard Shad; however, movement of Gizzard Shad between Lake Sharpe and Hipple Lake is unknown. To understand movement of Gizzard Shad, 40 adults (20 in 2014 and 20 in 2015) were implanted with acoustic telemetry tags. Passive receivers determined movement patterns and fish locations. Analysis included 28 individuals due to removal of mortalities and other restrictions. Tagged individuals were at large in Lake Sharpe from May 5, 2014 through April 11, 2017. Over 50% of tagged Gizzard Shad overwintered in Hipple Lake. Gizzard Shad moved larger distances in the summer (average 1.5 rkm/day) and fall (average 1.75 rkm/day) months but did not move substantially during winter (average 0.42 rkm/day) and spring (average 0.37 rkm/day) months. Overall, Hipple Lake appears to be an important habitat for Gizzard Shad within Lake Sharpe and should be prioritized for habitat conservation as connectivity between Hipple Lake and Lake Sharpe is being lost through siltation and emergent vegetation growth.

As a restoration measure, dam removal is expected to lead to ecological improvement. However, there is little understanding how dam removal affects lateral interactions across ecosystem boundaries. The transfer of aquatic resource subsidies into terrestrial food webs via the winged adult stages of aquatic insects is recognized as a key component in the functioning of riverine networks. Here, a quantitative review was performed to investigate the potential of dam removal to restore lateral connectivity with riparian ecosystems in terms of the production and dispersal of aquatic insect subsidies. Specifically, the functional trait composition of benthic invertebrate insect assemblages was analyzed to assess how the dispersal and life history of stream invertebrates are affected by dam removal. Functional trait responses to dam removal were quantified within the downstream, impoundment and upstream sections, utilizing extracted or calculated functional traits from a comprehensive search of empirical studies containing pre- and post-dam removal data along with the specific sampling distance from the dam (downstream and impoundment) or distance from the impoundment (upstream) and time from dam removal. The findings of this study suggest that the removal of small dams results in a more constant, rather than pulsed, supply of aquatic insects as resource subsidies for terrestrial consumers. Furthermore, results indicate an increase in potential aquatic prey dispersal extent into the terrestrial landscape in the downstream section and initially in the impoundment.

Monitoring water and sediment quality in freshwater ecosystems is essential for sustainable management and ecological protection. This study assessed heavy metal contamination in water and sediments from five sampling stations in Asejire Reservoir, Oyo State, Nigeria. A range of pollution indices was employed to quantify contamination levels. Principal Component Analysis (PCA) and Cluster Analysis (CA) were used to identify potential sources of pollution, while the Water Quality Index (WQI) provided an overall evaluation of water quality. The WQI score of 74.23 indicated generally good water quality, although localized contamination was observed. PCA results suggested that most heavy metals originated from anthropogenic activities, and CA grouped pollution sources into two main clusters. The geo-accumulation index showed low cadmium (Cd) levels at most stations, with slight to moderate pollution recorded at Station 5. Chromium (Cr), copper (Cu), and lead (Pb) exhibited moderate to strong pollution levels. Ecological risk assessment indicated no significant risk from Cr, low risk from Cu and Pb, and a very high ecological risk from Cd. The Heavy Metal Pollution Index (HPI), ranging from 290.35 to 294.75, further confirmed substantial human-related input. These findings highlight the need for routine monitoring and targeted remediation to prevent further degradation, safeguard aquatic ecosystems, and protect public health.

Eurasian watermilfoil (Myriophyllum spicatum) is an exotic vascular plant in North America and highly invasive in lacustrine environments. This plant forms dense, extensive beds that can interfere with recreational activities. Eurasian watermilfoil has been shown in laboratory experiments to cause mortality or low growth rates to several species of cyanobacteria, because of allelopathic molecules (fatty acids, polyphenols) released into the water by the plant. The allelopathic effect of Eurasian watermilfoil has never been studied in a natural setting. The main objective of this study was to verify whether a causal link between Eurasian watermilfoil and cyanobacteria could be established in two infested lakes of southern Québec, Canada. Some fatty acids or polyphenols (ellagic, nonanoic, octadecenoic and oleic acids) were detected in summer and autumn in the water, but in concentrations well below (30 to 35,000 times lower) the theoretical concentrations at which they reduce the growth of cyanobacteria. There was no evidence of allelopathic effects of Eurasian watermilfoil on the cyanobacterial assemblages. Other chemical and physical factors likely had greater influences on cyanobacterial assemblage composition than Eurasian watermilfoil, notably phosphorus concentration and water temperature. However, some cyanobacterial species known to be influenced by Eurasian watermilfoil, in particular Microcystis aeruginosa, were not specifically identified in this study, so caution must be exercised before concluding that there is no allelopathic effect.